There are cases where a vehicle uses information about a target object detected by an in-vehicle radar apparatus, to perform drive support by having various in-vehicle devices cooperate for avoiding an obstacle, and to control the vehicle speed and the distance to a preceding vehicle to travel while following the preceding vehicle. The radar apparatus irradiates, for example, a millimeter wave to a predetermined range in front of the vehicle, and receives a reflected wave reflected by a target in the irradiation range. Then, by analyzing the reception wave, the distance, relative speed, and direction (angle or lateral position) to the target are detected.
However, a radio wave such as a millimeter wave is reflected by an object other than the preceding vehicle or the detection target, such as a wall, a road surface, and a manhole, and hence, the reflected wave is received via a what-is-called “multipath”. This makes the detection difficult, especially for the direction of the target. For example, when the vehicle is traveling through a tunnel, the radio wave is reflected by a sidewall of the tunnel, which makes the vehicle detect a target on the sidewall side in front. Such a target detected by a reception wave received after being reflected by a wall is called a “mirror ghost”.
Since a mirror ghost does not need to be detected as a target, technologies have been considered to distinguish a mirror ghost from a preceding vehicle (see, for example, Patent Document 1). Patent Document 1 discloses a radar apparatus that sets a virtual wall beside a detected target to detect a mirror ghost based on the speed of another target symmetrically positioned with the target with respect to the virtual wall.
However, there are cases where the radar apparatus described in Patent Document 1 cannot detect a mirror ghost and a preceding vehicle separated from each other.
FIG. 1 is an example of diagrams illustrating a problem with a conventional radar apparatus. In FIG. 1(a), the radar apparatus of a vehicle separately detects a preceding vehicle and another target (mirror ghost) symmetrically positioned with respect to a virtual wall. Therefore, it is possible to detect that a reception wave reflected by the wall is not from the target, but from the mirror ghost. On the other hand, in FIG. 1(b), the radar apparatus of the vehicle detects a target about an intermediate point between the preceding vehicle and the mirror ghost. Such inconvenience tends to occur when the space between the preceding vehicle and the wall is narrow; the distance between the vehicle and the preceding vehicle is great; or, an angle formed between the direction of the mirror ghost and the direction of the preceding vehicle is small when viewed from the vehicle.
In such cases, the radar apparatus detects that a target is positioned in an intermediate direction (on the virtual wall) between the preceding vehicle and the mirror ghost. Consequently, the target itself is detected, but its direction is shifted.
Thus, the conventional radar apparatus has the problem in that it cannot distinguish a preceding vehicle from a mirror ghost, depending on a relative positional relationship among the preceding vehicle, the virtual wall, and the vehicle.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2009-133761